Method for controlling the temperature of a gas distribution plate in a process reactor

ABSTRACT

A plasma process reactor is disclosed that allows for greater control in varying the functional temperature range for enhancing semiconductor processing and reactor cleaning. The temperature is controlled by splitting the process gas flow from a single gas manifold that injects the process gas behind the gas distribution plate into two streams where the first stream goes behind the gas distribution plate and the second stream is injected directly into the chamber. By decreasing the fraction of flow that is injected behind the gas distribution plate, the temperature of the gas distribution plate can be increased. The increasing of the temperature of the gas distribution plate results in higher O 2  plasma removal rates of deposited material from the gas distribution plate. Additionally, the higher plasma temperature aids other processes that only operate at elevated temperatures not possible in a fixed temperature reactor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/944,503,filed Aug. 30, 2001, now U.S. Pat. No. 6,387,816, issued May 14, 2002,which is a continuation of application Ser. No. 09/514,820, filed Feb.28, 2000, now U.S. Pat. No. 6,323,133 B1, issued Nov. 27, 2001, which isa divisional of application Ser. No. 09/026,246, filed Feb. 19, 1998,now U.S. Pat. No. 6,132,552, issued Oct. 17, 2000.

BACKGROUND OF THE INVENTION

The present invention relates generally to process reactors used infabricating semiconductor devices and, more particularly, to the controlof the plasma temperature within the process reactor for improvedreactor fabrication and maintenance operations. Plasma process reactorsare used for both etching and depositing material on the surface of thesemiconductor substrate. In either case, a gas is injected into thechamber of the process reactor where it is ionized into a plasma foreither etching or reacting with the surface of the semiconductorsubstrate to form a desired pattern thereon. It is important to controlthe gas distribution into the reactor, as well as to control thetemperature of the gas in forming the plasma. Process reactors often usea thermally isolated dielectric plate to control the gas distributioninto the reactor. The gases are injected into the chamber on the backside of the dielectric plate and pass through gas inlet holes in theplate to get into the reaction zone.

The plate is thermally isolated because a backside gap is required toallow the process gases to flow behind the plate to the gas inlet holes.This makes the plate temperature and gas temperature difficult tocontrol as the process puts a heat load on the plate.

Attempts have been made to control the temperature by controlling thetemperature of the dielectric plate. Methods of adjusting or controllingthe temperature have been performed by adjusting the backside gap to beas small as possible, by controlling the temperature of the reactor walllocated behind it, or by cooling the dielectric plate, or anycombination of the three. The heat transfer between the plate and thetemperature control reactor wall occurs by conduction of the process gasas it flows through the narrow gap. The gas pressure, and not its flowrate, controls how much heat is transferred between the two surfaces.The plate temperature is controlled by the gas pressure, the reactorwall temperature, and the heat load on the plate from the processchamber.

A sample plasma process reactor 10 is depicted in the schematic diagramof FIG. 1. Plasma process reactor 10 includes a plasma chamber 12 inwhich is positioned a substrate holder 14. A semiconductor substrate 16is placed on substrate holder 14. A bias voltage controller 18 iscoupled to substrate holder 14 in order to bias the voltage to counterthe charges building up on semiconductor substrate 16. An etching gas isprovided through gas inlet 20, which is ionized by inductor back side22. Placed upon inductor inductor back side 22 is a plurality ofinductor elements 24 that is controlled by a current 26. Current 26causes an induction current to flow that generates an ionizing field onthe interior surface of inductor back side 22. The plasma then passesthrough a gas distribution plate 28, which is held in place with avacuum seal via O-ring 30, allowing a gas to pass through a plurality ofapertures 32. A second O-ring 34 is placed between the inductor backside 22 and gas distribution plate 28. A vacuum is created by a vacuumpump 36 for evacuating material and pressure from plasma chamber 12. Acontrol gate 38 is provided to allow a more precise control of thevacuum, as well as the evacuated material. An outlet 40 removes thematerial from the vacuum for disposal.

In this example, gas distribution plate 28 is made of a silicon nitridematerial. In certain desired oxide etch processes, it is required thatthe gas distribution plate 28 be cooled below 80° C. This cooling isaccomplished by cooling the reactor wall of plasma chamber 12 and issometimes called a window in this plasma etch reactor. The reactor wallis cooled to about 20° C. and the process gas is run through the backside gap. Unfortunately, the temperature of the gas distribution plate28 cannot be easily modified in this arrangement. The inability tocontrol the temperature causes other problems during different stages ofuse of the process reactor.

One problem is that cleaning of the interior cannot be easily performedsince the temperature is fixed as the gas distribution plate isthermally coupled to the reactor wall during cleaning. It is helpful torun the cleaning process at much higher temperatures than during theetching process, but such an effective cleaning temperature cannot beachieved since the temperature is controlled by the constant gas flow atthe gas distribution plate. Another problem is that processmodifications cannot be performed since only a set maximum temperatureis possible and no higher temperature is available that would allowdifferent processes to be performed that require hotter temperaturesthan those otherwise possible in a fixed-temperature reactor.

Accordingly, what is needed is a method and apparatus that overcome theprior problem of being unable to vary the temperature range of theprocess reactor for providing greater control over the process occurringin the processor reactor. The inability to vary the temperature rangealso hinders the cleaning ability of the reactor.

SUMMARY OF THE INVENTION

According to the present invention, a plasma process reactor isdisclosed that allows for greater control in varying the functionaltemperature range for enhancing semiconductor processing and reactorcleaning. The temperature is controlled by splitting the process gasflow from a single gas manifold that injects the process gas behind thegas distribution plate into two streams where the first stream goesbehind the gas distribution plate and the second stream is injecteddirectly into the chamber. By decreasing the fraction of flow that isinjected behind the gas distribution plate, the temperature of the gasdistribution plate can be increased. The increasing of the chambertemperature results in higher O₂ plasma cleaning rates of the depositson the hotter surfaces. Additionally, where other processes wouldbenefit from warmer gas distribution temperatures, the high gas flowallows higher temperatures to be achieved over the non-split flow of theprior art.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic diagram of a plasma process reactor according tothe prior art;

FIG. 2 is a schematic diagram of a plasma process reactor having a splitfold plasma manifold and injector according to the present invention;

FIG. 3 is a schematic diagram of a top plan view of a gas distributionring providing the secondary gas flow into the chamber;

FIG. 4 is an alternative embodiment of the gas flow ring used in theplasma process reactor of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

A high density plasma process reactor 100 is depicted in the schematicdiagram of FIG. 2. The reactor may have multiple plasma sources whereone source is for etching layers in a semiconductor substrate while theother source is for depositing a polymer. Reactor 100 is a low pressurereactor that operates at or below 50 milliTorr. Low pressure reactorsare desired as they avoid microscopic loading, where features of thesame size etch more slowly in dense patterns than in sparse patterns.The reactor 100 has separate controls for top and bottom power. The toppower is for energizing high density plasma sources and the bottom poweror bias source is for directing the plasma for etching and for directinga polymer for depositing. The high density plasma process reactor 100 ismodeled after an LAM 9100 TCP (transferred coupled plasma) etcher and anApplied Materials HDP 5300. High density plasma is defined as plasmahaving an ion density greater than 1×10¹⁰ per centimeter³ in a plasmageneration zone. Typically, high density plasmas range in ion densityfrom 10¹¹ to 10¹³ per cm³.

Reactor 100 increases the range of process results capable of beingobtained as well as improves the ability to clean the chamber by addinga second process gas flow inlet that avoids gas passing through the gasdistribution plate on the back side of the reactor. Reactor 100 issimilar in construction to that of the prior art reactor 10 in FIG. 1.Reactor 100 includes a chamber 112 in which is placed a substratesupport platform 114 that holds a semiconductor substrate 116. Aplurality of semiconductor substrates 116 can be placed upon substratesupport platform 114. The bottom bias source is controlled by voltagesupply 118 that either grounds substrate support platform 114 or holdsit at a selected voltage to attract the plasma generated within reactor100. A first process gas inlet 120 is provided that feeds process gaswithin a chamber formed by reactor back side 122 and gas distributionplate (or dielectric) 128. Gas distribution plate 128 further includes adielectric layer 129, placed on the reactor back side 122 of gasdistribution plate 128.

A plurality of inductive power sources 124, which is controlled by powersupply 126, is mounted to the reactor back side 122 for inductivelycoupling energy to form the plasma that is emitted through apertures 132in gas distribution plate 128. A first O-ring 130 is used to seal gasdistribution plate 128 in place within chamber 112 and a second O-ring134 is used to form the chamber between reactor back side 122 and gasdistribution plate 128. A vacuum is created by a vacuum pump 136 froevacuating material and pressure from plasma chamber 112. A control gate138 is provided to allow a more precise control of the vacuum, as wellas the evacuated material. An outlet 140 removes the material from thevacuum for disposal. Reactor 100 further includes a second process gasinlet 142 as well as an auxiliary oxygen inlet 144; both inlets providegas flow into chamber 112 and thus bypass gas distribution plate 128. Bysplitting the process gas flow into chamber 112 via first process gasinlet 120 and second process gas inlet 142, the fractional flowdecreases that flows behind the gas distribution plate 128, thusallowing the temperature of plate 128 to increase. Inlets 120, 142, and144 can be controlled by a mechanical valve (not shown) that iselectronically controlled to open and close at different times.

The second process gas inlet 142 actually feeds into a distribution ring146 (FIG. 3). In the embodiment of FIG. 2, a pair of distribution rings146, 148 are placed within the reactor, one above semiconductorsemiconductor substrate 116 and another substantially coplanar tosemiconductor substrate 116. In using distribution ring 146, it is anannular ring with gas vents that point downwardly towards semiconductorsubstrate 116. The distribution ring 146 is annular and thus provides aradial gas flow symmetrical to the semiconductor substrate 116. Thealternative distribution ring 148, which may be used in tandem with thefirst ring, has jets 150 that direct the gas flow upward and radiallyinward for uniform distribution to semiconductor substrate 116.

The use of the additional inlet valves allows reactor 100 to improve itscleaning ability, as well as provide process modifications. When theprocess gas is 100% injected through the side, the cooling of thedielectric layer 129 on gas distribution plate 128 diminishes and the O₂plasma can now clean deposits from the gas distribution plate 128,because it is thermally uncoupled from the reactor back side 122 duringthe cleaning step. Further, residue, such as fluorocarbon polymers, isquickly and more efficiently cleaned off of gas distribution plate 128because of the higher temperature.

Process modifications are possible now in that if conditions requirehigh gas flows to occur, but also require a warmer gas distributionplate, the split flow allows the plate to operate at higher temperaturesthan the prior method of just passing process gas through gasdistribution plate 128.

Importantly, the change in gas temperature is inversely-proportional tothe change in pressure within chamber 112. Accordingly, by reducing thepressure behind gas distribution plate 128, the temperature of the gasflow can increase by bypassing gas distribution plate 128.

FIG. 3 is a bottom plan view of a second inlet gas distribution ring146. Distribution ring 146 includes an annular gas vent 152 that has aplurality of holes 154 distributed around the inner perimeter. The holescan be directed to point either perpendicular to the plane ofdistribution ring 146 or to point slightly inwardly radially towards theaxis of the annular gas vent 152. An inlet connector 156 is provided toattach distribution ring 146 to the interior of chamber 112. FIG. 4depicts an alternative embodiment of the distribution ring 146. In thisembodiment, distribution ring 146 has a square or polygonal shaped gasvent 158. A plurality of holes 154 is provided along the bottom surfaceof gas vent 158. Again, an inlet connector 156 is provided to connectdistribution ring 146 to the second process gas inlet 142 within chamber112. Either ring of FIG. 3 or FIG. 4 can be placed in the position ofdistribution ring 146 in FIG. 2. Additionally, either ring can be placedin a position of distribution ring 148 having jets 150 that aresubstantially coplanar with the semiconductor substrate 116.

Referring back to the cleaning operation used to clean plasma processreactor 100, the oxygen is introduced at a partial pressure shown inTable I below:

TABLE I PRESSURE AT GAS CHAMBER FLOWS DISTRIBUTION PLATE 128 PRESSUREGASES (sccm) (Torr) (mTorr) C₂HF₅ 15 30-40 5-50 N₂ 5 CHF₃ 15 CH₂F₂ 15

The approximate temperature behind the gas distribution plate 128 isT₁₂₈=80° C. For another example, if the gas flow is split equally(50/50) between the gas distribution plate 128 and the secondary secondprocess gas inlet 142, the pressure behind gas distribution plate 128 isbetween 15-20 Torr, with a temperature approximately T₁₂₈=110° C. As theflow increases at the second process gas inlet valve 142, thetemperature can increase from 50° to 250° C. Table II provides thevalues for when the flow is either 100% through first process gas inlet120 or second process gas inlet 142:

TABLE II PRESSURE 100% through Inlet 120 100% through Inlet 142 Behind30-500 mTorr 5-500 mTorr Gas Distribution Plate 128 In Chamber  5-500mTorr 5-500 mTorr

The chamber pressure is independent of the pressure behind gasdistribution plate 128. The pressure for 100% of the flow through firstprocess gas inlet 120 is dependent on O₂ flow rates shown in Table I.

The present invention may be employed to fabricate a variety of devicessuch as, for example, memory devices. These other devices are notnecessarily limited to memory devices but can include applications,specific integrated circuits, microprocessors, microcontrollers, digitalsignal processors, and the like. Moreover, such devices may be employedin a variety of systems, such systems including, but not limited to,memory modules, network cards, telephones, scanners, facsimile machines,routers, copying machines, displays, printers, calculators, andcomputers, among others.

Although the present invention has been described with reference to aparticular embodiment, the invention is not limited to the describedembodiment. The invention is limited only by the appended claims, whichinclude within their scope all equivalent devices or methods whichoperate according to the principles of the invention as described.

What is claimed is:
 1. A temperature control method for a plasma withina plasma process reactor having a first and a second region and a singleprocess gas flow stream thereinto, comprising: providing a first gasdistribution plate having a top surface and a bottom surface with aplurality of apertures therethrough, said first gas distribution plateseparating said first region from said second region and connecting saidfirst and second regions by said plurality of apertures; splitting thesingle process gas flow stream into a first gas flow stream and a secondgas flow stream; introducing the first gas flow stream into said firstregion of the plasma process reactor; and introducing the second gasflow stream into said second region of the plasma process reactor, saidintroducing the second gas flow stream into the second regionsubstantially bypassing the first region.
 2. The method of claim 1,wherein the first and second gas flow streams are each introduced as afraction of the single process gas flow stream, the method furthercomprising: varying a temperature within at least one of the first andsecond regions by varying a fraction of the first gas flow stream whichflows into the first region.
 3. The method of claim 2, furthercomprising: forming a partial pressure in the first region such that atemperature of plasma increases as the partial pressure decreases. 4.The method of claim 1, further comprising evacuating the plasma processreactor.
 5. The method of claim 1, further comprising: increasing atemperature of surfaces cooled by gases in the first region byintroducing the second gas flow stream into the second regionsubstantially bypassing the first region.